Turbines are widely used in industrial and commercial operations. A typical commercial steam or gas turbine used to generate electrical power includes alternating stages of stationary and rotating airfoils or blades. For example, stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, and rotor blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as but not limited to steam, combustion gases, or air, flows through the turbine, and the stator vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotor blades to impart motion to the rotor blades, thus turning the rotor and performing work.
Compressed working fluid that leaks around or bypasses the rotor blades reduces the efficiency of the turbine. To reduce the amount of compressed working fluid that bypasses the rotor blades, the casing may include stationary shroud segments that surround each stage of rotor blades, and each rotor blade may include a tip cap at an outer radial tip that reduces the clearance between the shroud segments and the rotor blade. Although effective at reducing or preventing leakage around the rotor blades, the interaction between the shroud segments and the tip caps may result in elevated local temperatures that may reduce the low cycle fatigue limits and/or lead to increased creep at the tip caps. As a result, a cooling media may be supplied to flow inside each rotor blade before flowing through cooling passages in the tip cap to provide film cooling over the tip cap of the rotor blade.
In particular designs, each tip cap may include an outer surface or tip plate that is at least partially surrounded by a rim. The rim and the tip plate may at least partially define a tip cavity, also known as a squealer tip cavity, between the rim, the tip plate, and the surrounding shroud segments. In this manner, the cooling media supplied to the squealer tip cavity may remove heat from the tip cap before flowing over the rim and out of the squealer tip cavity. However, excessive cooling media that flows over the suction side of the rotor blade may disrupt the flow of the compressed working fluid over the rotor blades and/or reduce the operating efficiency of the turbine. As a result, an improved rotor blade and a method for cooling the rotor blade would be useful.